Interactions of selected ketone flavours with porcine myofibrillar proteins: The role of molecular structure of flavour compounds

Myofibrillar protein hydrolysis under hydroxyl radical oxidative stress: Structural changes and their impacts on binding to selected aldehydes

In this study, a hydroxyl radical oxidation system was established to simulate the oxidation process in fermented meat products. This system was employed to examine the structural changes in myofibrillar proteins (MPs) resulting from tryptic hydrolysis after a hydroxyl radical oxidative regime. The effect of these changes on the ability of MPs to bind selected aldehydes (3-methyl butanal, pentanal, hexanal, and heptanal) was also investigated. Moderate oxidation (H2O2 ≤ 1.0 mM) unfolded the structure of MPs, facilitating trypsin-mediated hydrolysis and increasing their binding capacity for the four selected aldehydes. However, excessive oxidation (H2O2 ≥ 2.5 mM) led to cross-linking and aggregation of MPs, inhibiting trypsin-mediated hydrolysis. The oxidised MPs had the best binding capacity for heptanal. The interaction of the oxidised trypsin-hydrolysed MPs with heptanal was driven by hydrophobic interactions. The binding of heptanal affected the structure of the oxidised trypsin-hydrolysed MPs and reduced their α-helix content.

Characterization of the flavor profile and dynamic changes in Chinese traditional fish sauce (Yu-lu) based on electronic nose, SPME-GC-MS and HS-GC-IMS

In this study, flavor characteristics and dynamic change of Chinese traditional fermented fish sauce (Yu-lu) with different fermentation time (2, 4, 6, 8, and 12 months) were analyzed. The electronic nose analyses confirmed a notable flavor change in fish sauce samples from different stages. During the 12-months fermentation, the total volatile compounds in fish sauce increased from 3.9 mg/L to 13.53 mg/L. Acids, aldehydes, esters and phenols were the main aroma substances and their contents gradually increased during the fermentation process. The PCA of GC-MS and GC-IMS showed that fish sauce samples from different fermentation periods can be well distinguished. A total of 110 volatile compounds identified by GC-MS, and 102 volatile compounds were detected by GC-IMS. Among them, 13 compounds were identified by both GC-MS and GC-IMS. The most varieties (49) of volatiles appeared after 8 months of fermentation. The odor activity value (OAV) analysis showed that 10 volatile compounds were considered as characteristic flavor in traditional fish sauce. The variable influence on projections (VIPs) in PLS-DA models constructed by GC-MS and GC-IMS identified 5 and 10 volatile compounds as biomarkers, respectively. Our results revealed the dynamic changes of characteristic flavor in fish sauce in combination of GC-MS and GC-IMS, which provides theoretical basis for the production and flavor regulation of fish sauce.

Ultrasonic treatment enhanced the binding capacity of volatile aldehydes and pearl mussel (Hyriopsis cumingii) muscle: Investigation of underlying mechanisms

This study was aim to investigate the influencing mechanism of ultrasonic treatment on the interaction between volatile aldehydes and myosin. The results showed that when the mass concentration ratio of myosin to heptanal/hexanal was 1:0.3, ultrasonic treatment could enhance the binding capacity of myosin to heptanal/hexanal, especially the binding of myosin to hexanal. The entropy and enthalpy values of their interaction were negative, indicating that the interaction was mainly driven by hydrogen bond and van der Waals force. After ultrasonic treatment, the fluorescence wavelength of myosin-heptanal/hexanal complex was redshifted, the α-helix content was increased, while its roughness values, particle size and the polydispersity index were decreased. These demonstrated that ultrasonic treatment was conducive to myosin binding to heptanal/hexanal, thereby restraining the release of volatile flavor compounds from myosin, which could provide new insights for the regulation of volatile flavor compounds.

Recent advances and challenges in the interaction between myofibrillar proteins and flavor substances

Myofibrillar proteins are an important component of proteins. Flavor characteristics are the key attributes of food quality. The ability of proteins to bind flavor is one of their most fundamental functional properties. The dynamic balance of release and retention of volatile flavor compounds in protein-containing systems largely affects the sensory quality and consumer acceptability of foods. At present, research on flavor mainly focuses on the formation mechanism of flavor components, while there are few reports on the release and perception of flavor components. This review introduces the composition and structure of myofibrillar proteins, the classification of flavor substances, the physical binding and chemical adsorption of myofibrillar proteins and volatile flavor substances, as well as clarifies the regulation law of flavor substances from the viewpoint of endogenous flavor characteristics and exogenous environment factors, to provide a theoretical reference for the flavor regulation of meat products.

Drivers of the In-Mouth Interaction between Lupin Protein Isolate and Selected Aroma Compounds: A Proton Transfer Reaction-Mass Spectrometry and Dynamic Time Intensity Analysis

Plant proteins often carry off-notes, necessitating customized aroma addition. In vitro studies revealed protein-aroma binding, limiting release during consumption. This study employs in vivo nose space proton transfer reaction-time-of-flight-mass spectrometry and dynamic sensory evaluation (time intensity) to explore in-mouth interactions. In a lupin protein-based aqueous system, a sensory evaluation of a trained "green" attribute was conducted simultaneously with aroma release of hexanal, nonanal, and 2-nonanone during consumption. Results demonstrated that enlarging aldehyde chains and relocating the keto group reduced maximum perceived intensity (Imax_R) by 71.92 and 72.25%. Protein addition decreased Imax_R by 30.91, 36.84, and 72.41%, indicating protein-aroma interactions. Sensory findings revealed a perceived intensity that was lower upon protein addition. Aroma lingering correlated with aroma compounds' volatility and hydrophobicity, with nonanal exhibiting the longest persistence. In vitro mucin addition increased aroma binding four to 12-fold. Combining PTR-ToF-MS and time intensity elucidated crucial food behavior, i.e., protein-aroma interactions, that are pivotal for food design.

Influence of seaweed dietary fibre as a potential alternative to phosphates on the quality profiles and flavour attributes of frankfurters

This study primarily aimed to investigate the influence of seaweed dietary fibre (SDF), as a potential alternative to phosphates, on the quality profiles and flavour attributes of frankfurters. The results revealed that SDF addition can significantly improve the cooking yield and texture characteristics of phosphate-free frankfurters (P < 0.05), and 1.00% SDF proved to be the optimal concentration for replacing phosphates in frankfurters. Moreover, electronic nose and electronic tongue analyses demonstrated that SDF incorporation potentially influences the aroma and taste of phosphate-free frankfurters. Furthermore, volatile compound analysis revealed that SDF addition potentially compensates for the decrease in volatile flavour compound content caused by phosphate deficiency. Generally, our results indicate that SDF can be successfully applied as a potential alternative to phosphates and subsequently improve the quality profiles and flavour attributes of phosphate-free frankfurters. Moreover, they provide valuable theoretical guidance for the processing of phosphate-free emulsified meat products.

Decoding the interaction mechanism between bis(2-methyl-3-furyl) disulfide and oral mucin

The interactions between mucin and aroma compounds have been shown to affect aroma perception. This study aimed to investigate the binding behavior between mucin and bis(2-methyl-3-furyl) disulfide and reveal the interaction mechanism at different pH levels. Based on our results, the binding percentages between mucin and bis(2-methyl-3-furyl) disulfide ranged from 37.03 % to 71.87 % at different contents. The complexes formation between mucin and bis(2-methyl-3-furyl) disulfide was confirmed by turbidity, particle size, zeta-potential, and surface hydrophobicity analyses. According to the results of multispectral techniques and molecular dynamic simulation, mucin could interact with bis(2-methyl-3-furyl) disulfide by hydrogen bonding, hydrophobic interactions, and van der Waals force. Furthermore, the binding constants of mucin to bis(2-methyl-3-furyl) disulfide were 1.26 × 103, 1.14 × 103, and 9.13 × 103 L mol-1 at pH 5.0, 7.0, and 8.5, respectively. These findings contribute to the comprehensive knowledge on the interaction mechanism between bis(2-methyl-3-furyl) disulfide and mucin, providing insights for flavor modulation in meat products.

Correlation study on microbial communities and volatile flavor compounds in cigar tobacco leaves of diverse origins

To elucidate the significant influence of microorganisms on geographically dependent flavor formation by analyzing microbial communities and volatile flavor compounds (VFCs) in cigar tobacco leaves (CTLs) obtained from China, Dominica, and Indonesia. Microbiome analysis revealed that the predominant bacteria in CTLs were Staphylococcus, Aerococcus, Pseudomonas, and Lactobacillus, while the predominant fungi were Aspergillus, Wallemia, and Sampaiozyma. The microbial communities of CTLs from different origins differed to some extent, and the diversity and abundance of bacteria were greater than fungi. Metabolomic analysis revealed that 64 VFCs were identified, mainly ketones, of which 23 VFCs could be utilized to identify the geographical origins of CTLs. Sixteen VFCs with OAV greater than 1, including cedrol, phenylacetaldehyde, damascone, beta-damascone, and beta-ionone, play important roles in shaping the flavor profile of CTLs from different origins. Combined with the correlation analysis, bacterial microorganisms were more closely related to key VFCs and favored a positive correlation. Bacillus, Vibrio, and Sphingomonas were the main flavor-related bacteria. The study demonstrated that the predominant microorganisms were essential for the formation of key flavor qualities in CTLs, which provided a theoretical reference for flavor control of CTLs by microbial technology. KEY POINTS: • It is the high OAV VFCs that determine the flavor profile of CTLs. • The methylerythritol phosphate (MEP) pathway and the carotenoid synthesis pathway are key metabolic pathways for the formation of VFCs in CTLs. • Microbial interactions influence tobacco flavor, with bacterial microorganisms contributing more to the flavor formation of CTLs.

Flavor Characteristics of Umami Peptides from Wuding Chicken Revealed by Molecular Dynamics Simulation

Wuding chicken is famous for its delicious meat, and HLEEEIK, LDDALR, and ELY were jointly extracted from different processing stages of Wuding chicken. However, whether these peptides can be used as umami supplements is unclear. The sensory evaluation tests were used to study the taste characteristics. The secondary structure of the peptides and their interaction with T1R1/T1R3 were predicted by the circular dichroism spectrum and molecular dynamics simulation. The umami threshold was 0.03125 to 0.06250 mg/mL, all of which could increase umami, saltiness, sweetness, and mask bitterness. Compared with HLEEEIK, the frequency of umami active fragments and the improvement rate of the umami score of EEE increased by 133.35% and 40.09%, respectively. Peptides were dominated by umami taste according to sensory analysis, among which EE-3 (3.18) has the highest umami intensity followed by LR-4 (2.58), HK-7 (2.13), and EY-3 (1.82). The main secondary structure of umami peptides was β-folding, and Tyr74, Arg323, Arg272, and Gln35 were the key amino acid residues for binding of umami peptides to the receptor. This study further elucidated that the umami intensity of the peptides could be altered by changing the sequence composition of the peptides, which enhanced our understanding of the complex flavor properties of umami peptides.

Synergistic Effects of High-Intensity Ultrasound Combined with L-Lysine for the Treatment of Porcine Myofibrillar Protein Regarding Solubility and Flavour Adsorption Capacity

This study aimed to investigate the synergistic effects of high-intensity ultrasound (0, 5, 10, 15, and 20 min) in combination with L-lysine (15 mM) on improving the solubility and flavour adsorption capacity of myofibrillar proteins (MPs) in low-ion-strength media. The results revealed that the ultrasound treatment for 20 min or the addition of L-lysine (15 mM) significantly improved protein solubility (p < 0.05), with L-lysine (15 mM) showing a more pronounced effect (p < 0.05). The combination of ultrasound treatment and L-lysine further increased solubility, and the MPs treated with ultrasound at 20 min exhibited the best dispersion stability in water, which corresponded to the lowest turbidity, highest absolute zeta potential value, and thermal stability (p < 0.05). Based on the reactive and total sulfhydryl contents, Fourier transform infrared spectroscopy, and fluorescence spectroscopy analysis, the ultrasound treatment combined with L-lysine (15 mM) promoted the unfolding and depolymerization of MPs, resulting in a larger exposure of SH groups on the surface, aromatic amino acids in a polar environment, and a transition of protein conformation from α-helix to β-turn. Moreover, the combined treatment also increased the hydrophobic bonding sites, hydrogen-bonding sites, and electrostatic effects, thereby enhancing the adsorption capacity of MPs to bind kenone compounds. The findings from this study provide a theoretical basis for the production and flavour improvement of low-salt MP beverages and the utilisation of meat protein.

The dynamic change of flavor characteristics in Pacific oyster (Crassostrea gigas) during depuration uncovered by mass spectrometry-based metabolomics combined with gas chromatography-ion mobility spectrometry (GC-IMS)

The flavor of Pacific oyster (Crassostrea gigas) significantly changed during the depuration process. This work aimed to explore the mechanism of flavor changes during the 72 h depuration by metabolomics combined with gas chromatography-ion mobility spectrometry (GC-IMS). The metabolomics analysis indicated that carbohydrate metabolism was more affected in the early stage of depuration, including the citrate cycle, glyoxylae and dicarboxylate metabolism, etc. After 72 h depuration, it affected mainly the metabolism of global and overview maps and nucleoside metabolism, etc. The equivalent umami concentration (EUC) value was calculated and exhibited a gradual increase following a 48 h depuration. The GC-MS results revealed that the content of furans was the highest, and the content of aldehydes, ketones, and alcohols was the lowest after 48 h depuration, while the content of aldehydes, ketones, and alcohols increased after 72 h depuration. All these results suggested the depuration period was recommended to be controlled within 48 h.

Unravelling the interaction between α-SOH and myofibrillar protein based on spectroscopy and molecular dynamics simulation

This work systematically investigated the dose-response interaction between hydroxy-α-sanshool (α-SOH) and pork myofibrillar proteins (MPs) via spectroscopy, molecular docking, and molecular dynamics simulation methods. Results showed that MPs bound with low α-SOH can enhance the surface hydrophobicity and particle size of MPs, whereas high concentrations were exactly the opposite. The main interaction force in α-SOH/MPs complex changed from hydrophobic to hydrogen bonding with increased α-SOH. α-SOH causes tryptophan quenching and bring about a red shift at low concentration, as well as to promote α-helix conversion into β-sheet in MPs. Simultaneously, molecular docking and dynamics simulations verified that hydrogen bonding and hydrophobic forces were the main contributors to α-SOH/MPs complex, indicating that the binding of α-SOH with MPs proceeded spontaneously with high intensity, in which TYR286 contributed the most significant energy. Therefore, revealing the binding mechanism of α-SOH and MPs can contribute to the deep processing of numbing meat products.

Comprehensive binding analysis of glycated myosin with furan derivatives via glucose by means of multi-spectroscopy techniques and molecular docking simulation

Myosin is an ideal binding receptor for aroma compounds and its functional properties are easily affected by glucose. The study comprehensively clarified the effects of glucose glycation-induced structural modifications of myosin on its binding ability with furan derivatives, including 2-methylfuran, 2-furfural, and 2-furfurylthiol. The results demonstrated that the binding levels of furan derivatives were obviously affected by the glycation levels of myosin due to the changes of myosin structure and surface. The increased glycation levels caused the unfolding of myosin structure and accelerated the aggregation, as were exhibited by the data of zeta potential, particle size, microstructure, and secondary structure. The glycated myosin with wrinkled surfaces favored the significant increase of hydrophobic interactions (31.59-69.50 μg), the more exposure of amino acid residues (3459-6048), the formation of free sulfhydryl groups (16.37-20.58 mmol/104g) and hydrogen bonds. These key (non)covalent linkages accounted for the generation of glycated myosin-odorants complex, including 2-furfurylthiol (29.17-47.87 %), thus enhancing the resultant binding ability as evidenced by the free furan derivatives concentrations, fluorescence quenching and molecular docking simulation analysis. The glycated myosin for 8 h bound highest concentrations of furan derivatives. The results will provide comprehensive data on the retention of aroma compounds in meat products.

Identification of umami peptides from Wuding chicken by Nano-HPLC-MS/MS and insights into the umami taste mechanisms

Wuding chicken is popular with consumers in China because of its umami taste. This study aimed to identify novel umami peptides from Wuding chicken and explore the taste mechanism of umami peptides. The molecular masses and amino acid compositions of peptides in Wuding chicken were identified by nano-scale liquid chromatography-tandem mass spectrometry (Nano-HPLC-MS/MS). The taste characteristics of the peptides synthesized by the solid-phase method were evaluated by sensory evaluation combined with electronic tongue technology. The secondary structure of the peptides was further analyzed by circular dichroism (CD), and the relationship between the structure and taste of the peptides was elucidated by molecular docking. The results showed that eight potential umami peptides were identified, among which FVT (FT-3), LDF (LF-3), and DLAGRDLTDYLMKIL (DL-15) had distinct umami tastes, and FT-3 had the highest umami intensity, followed by LF-3 and DL-15. The relative contents of β-sheets in the three umami peptides were 55.20%, 57.30%, and 47.70%, respectively, which were the key components of Wuding chicken umami peptides. In addition to LF-3 embedded in the cavity-binding domain of the TIR1, both FT-3 and DL-15 were embedded in the venus flytrap domain (VFTD) of the T1R3 to bind the umami receptor T1R1/T1R3. The main binding forces between the umami peptides and the umami receptor T1R1/T1R3 relied on hydrogen bonds and hydrophobic interactions, and the key amino acid residues of the combination of umami peptides and the umami receptor T1R1/T1R3 were Glu292, Asn235, and Tyr262.

Probing the mechanism of interaction between capsaicin and myofibrillar proteins through multispectral, molecular docking, and molecular dynamics simulation methods

The interaction between myofibrillar proteins (MPs) and capsaicin (CAP) was investigated using multispectral, molecular docking, and molecular dynamics simulation methods. The resulting complex increased the hydrophobicity of the tryptophan and tyrosine microenvironment as revealed by fluorescence spectral analysis. The fluorescence burst mechanism study indicated that the fluorescence burst of CAP on the MPs was a static one (Kq = 1.386 × 10¹² m^-1s^-1) and that CAP could bind with MPs well (Ka = 3.31 × 10⁴ L/mol, n = 1.09). The analysis of circular dichroism demonstrated that the interaction between CAP and MPs caused a decrease in the α-helical structure of MPs. The complexes formed exhibited lower particle size and higher absolute ζ potential. Furthermore, hydrogen bonding, van der Waals forces, and hydrophobic interactions were found to be the primary factors facilitating the interaction between CAP and MPs, as suggested by molecular docking models and molecular dynamics simulations.

Comprehensive Multi-Spectroscopy and Molecular Docking Understanding of Interactions between Fermentation-Stinky Compounds and Mandarin Fish Myofibrillar Proteins

The release of flavor compounds is a critical factor that influences the quality of fermented foods. A recent study investigated the interactions between four fermentation-stinky compounds (indole, isovaleric acid, dimethyl disulfide, and dibutyl phthalate) and myofibrillar proteins (MPs). The results indicated that all four fermentation-stinky compounds had different degrees of binding to MPs, with dibutyl phthalate and dimethyl disulfide exhibiting stronger interactions. Reduced hydrophobicity enhanced these interactions. Multi-spectroscopy showed that static fluorescence quenching was dominant in the MPs-fermentation-stinky compound complexes. The interaction altered the secondary structure of MPs, predominantly transitioning from β-sheets to α-helix or random coil structures via hydrogen bond interactions. Molecular docking confirmed that these complexes maintained steady states due to stronger hydrogen bonds, van der Waals forces, ionic bonds, conjugate systems, and lower hydrophobicity interactions. Hence, it is a novel sight that the addition of hydrophobic bond-disrupting agents could improve the flavor of fermented foods.

Exploration of molecular interaction between different plant proteins and 2-pentylfuran: based on multiple spectroscopy and molecular docking

BACKGROUND

Soy protein, peanut protein and wheat protein are commonly applied in plant-based products, but specific off-odor makes it difficult for consumers to accept, with 2-pentylfuran being one of the most representative flavors. In this study, 2-pentylfuran was employed as an example to explore the behavior and mechanism of the three proteins in absorbing off-odors.

RESULTS

Gas chromatographic-mass spectrometric analysis indicated that different plant proteins were able to adsorb 2-pentylfuran. Circular dichroism proved 2-pentylfuran could drive the α-helix to β-sheet transition of soy protein, which was not obvious in peanut protein or wheat protein. Ultraviolet spectroscopy tentatively determined that 2-pentylfuran caused changes in the tyrosine and tryptophan microenvironments of different plant proteins, which were further evidenced by synchronous fluorescence at fixed wavelength intervals of 15 nm and 60 nm. Static quenching of protein intrinsic fluorescence indicated that they formed a stable complex with 2-pentylfuran, except for wheat protein (dynamic quenching).

CONCLUSION

The various conformations of the three proteins are the main reason for the difference in flavor retention of protein. Soy protein, peanut protein and wheat protein adsorbing 2-pentylfuran relies on non-covalent forces, especially hydrophobic interactions, maintained between the protein and 2-pentylfuran. © 2023 Society of Chemical Industry.

Non-covalent interactions of selected flavors with pea protein: Role of molecular structure of flavor compounds

The influence of the molecular structures of flavor compounds (specifically, variations in chain length and functional groups) on the binding of the flavor compounds (Z)-2-penten-1-ol, hexanal, and (E)-2-octenal to pea protein was investigated. The results showed that the molecular structures of the flavor compounds strongly influenced their binding affinity for pea protein. Specifically, (E)-2-octenal exhibited a higher binding affinity and a higher Stern-Volmer constant with pea protein than both hexanal and (Z)-2-penten-1-ol. Thermodynamic analysis indicated that the flavor compound-pea protein interactions were spontaneous. Hydrophobic interactions were dominant in the non-covalent interactions between (E)-2-octenal/(Z)-2-penten-1-ol and pea protein, whereas hydrogen bonding was dominant in the non-covalent interactions between hexanal and pea protein. Surface hydrophobicity measurements, the use of bond-disrupting agents, and molecular docking further supported the hypothesis that hydrogen bonding, as well as hydrophobic interactions, occurred between the flavor compounds and pea protein.

Influence of Proteolysis on the Binding Capacity of Flavor Compounds to Myofibrillar Proteins

Proteolysis occurs extensively during postmortem aging, enzymatic tenderization and fermentation of meat products, whereas less is understood regarding how proteolysis affects meat flavor. Myofibrillar proteins (MP) were extracted from beef longissimus dorsi muscle and subsequently treated with three commercial proteases. The effect of proteolysis on the interactions between the treated MP and butyraldehyde, 2-pentanone, octanal and 2-octanone was investigated. The progress of proteolysis increased the degree of hydrolysis (DH) and the surface hydrophobicity but decreased the turbidity and particle size. Fluorescence-quenching analysis results indicated that the enzymatic treatment generally increased the quenching constant (Ksv) between the treated MP and ketones but decreased the Ksv between the treated MP and aldehydes, and the papain treatment changed the Ksv value to a larger degree than treatment with proteinase K and bromelain. The adsorption assay showed that the proteinase K treatment largely increased the adsorption capacity of the MP to octanal (by 15.8−19.3%), whereas the bromelain treatment significantly reduced the adsorption capacity of the treated MP to butyraldehyde (by 6.0−7.9%) and 2-pentanone (by 9.7−11.9%). A correlation analysis demonstrated a strong positive correlation (0.859, p < 0.05) between the DH of the MP and the adsorption ability of the treated MP to octanal. This study highlighted the significant but complex influence of proteolysis on MP binding capacity to flavor compounds.

Effect of sodium bicarbonate and sodium chloride on aggregation and conformation of pork myofibrillar protein

To investigate the effect of sodium bicarbonate instead of sodium chloride, the changes in pH, turbidity, aggregation, and conformation of myofibrillar protein solution with various amounts of sodium chloride and sodium bicarbonate were studied. When the sodium bicarbonate was increased from 0% to 0.4%, accompanied by the sodium chloride being decreased from 2.0% to 0.8%, the pH increased about 1.20 unites; the absolute values of the Zeta potential, active sulfhydryl, and surface hydrophobicity increased significantly (p < 0.05); and the turbidity, particle size, and Ca²⁺-ATPase activity decreased significantly (p < 0.05). In addition, the Mg²⁺-ATPase activity was not significantly different (p > 0.05) when increasing sodium bicarbonate, implying that sodium bicarbonate did not affect the actin. Overall, the results indicated that an increase in sodium bicarbonate could improve solubility, expose more hydrophobic residues and sulfhydryl groups, and induce Ca²⁺-ATPase inactivation and protein unfolding, leading the myofibrillar protein to denaturation easily.

Modulating the aggregation of myofibrillar protein to alleviate the textural deterioration of protein gels at high temperature: The effect of hydrophobic interactions

In this study, the strategy of utilizing a model hydrophobic molecule, octenyl succinic anhydride (OSA), to inhibit over-aggregation of MP during heating, aiming to alleviate high temperature-induced textural deterioration of MP gels, was proposed, and a series of experiments were conducted to verify the effectiveness. The results showed that the effect was positively dependent on the concentrations of OSA. The addition of OSA at a concentration of 4 g/kg to 24 g/kg delayed the gelation temperature of MP, as confirmed by the DSC results, and inhibited the aggregation of MP through hydrophobic interactions between OSA and MP, as revealed by fluorescence and FTIR spectroscopy. Furthermore, when the concentration of OSA increased from 4 g/kg to 12 g/kg, the controlled aggregation of MP improved the gel properties of MP formed at high temperature, but when the concentration reached 24 g/kg, the protein aggregation was too inhibited to form developed gel networks.

The effects of sodium chloride on proteins aggregation, conformation and gel properties of pork myofibrillar protein Running Head: Relationship aggregation, conformation and gel properties

The objective of this study was to evaluate relationship with aggregation, secondary structures and gel properties of pork myofibrillar protein with different sodium chloride (1%, 2% and 3%). When the sodium chloride increased from 1 to 3%, the active sulfhydryl, surface hydrophobicity, hardness and cooking yield of myofibrillar protein were increased significantly (p < 0.05), the particle size, total sulfhydryl and Zeta potential were decreased significantly (p < 0.05), these meant the aggregations of pork myofibrillar protein were decreased. The changes of proteins aggregation induced the strongest intensity band of Amide I shifted up from 1660 cm^-1 to 1661 cm^-1, meanwhile, the β-sheet structure content was increased significantly (p < 0.05) with the sodium chloride increased. From the above, the lower proteins aggregation and higher β-sheet structure content could improve the water holding capacity and texture of pork myofibrillar protein gel.

Profiling the interaction of Al(III)-GFLX complex, a potential pollution risk, with bovine serum albumin

Fluoroquinolone antibiotics (FQs), a new class of pollutants that seriously threaten human health through environmental and food residues, have aroused wide public concern. However, little attention has been paid to the potential toxicity of FQs' metal complex. Here, we firstly explore the proof-of-concept study of FQs' metal complex to bind bovine serum albumin (BSA) using systematical spectroscopic approaches. In detail, we have found that the complex of Al³⁺ with gatifloxacin (Al(III)-GFLX complex) can effectively bind to BSA via electrostatic interaction in PBS buffer (pH = 7.4, 1×), resulting in the formation of Al(III)-GFLX-BSA complex. The negative value of ΔG shows that the binding of Al(III)-GFLX complex to BSA is a spontaneous process. Circular dichroism spectra verify that Al(III)-GFLX complex effectively triggers the conformation changes of BSA's secondary structure. It has been proved that the interaction of small molecule with serum albumin has a significant effect on their in vivo biological effects such as absorption, distribution, metabolism, and excretion, and etc. Therefore, the results of this paper may offer a valuable theoretical basis for establishing safety standards of FQs' metal complex to ensure food and environmental health.

Effect of alkyl distribution in pyrazine on pyrazine flavor release in bovine serum albumin solution

The flavor release mechanism related to the interaction of aroma compounds with proteins is still unclear. In this study, the interaction of protein with pyrazine homologues, such as 2-methylpyrazine (MP), 2,5-dimethylpyrazine (DP), 2,3,5-trimethylpyrazine (TRP) and 2,3,5,6-tetramethylpyrazine (TEP), was investigated to elucidate the effect of alkyl distribution in a pyrazine ring on its flavor release in bovine serum albumin (BSA) solution (pH 7.4). The results of SPME-GC-MS indicated that methyl distribution in a pyrazine ring significantly affected its release from BSA solution. The pyrazines released from BSA solution with an increasing order of MP, DP, TRP and TEP. The inhibition mechanism of alkyl-pyrazine release was further elucidated by the interaction between alkyl-pyrazines and BSA using multiple spectroscopic methods. The non-covalent interaction between alkyl-pyrazines and BSA was confirmed as the main interaction force by the value of the bimolecular quenching constant (K q > 2 × 1010 L mol-1 s-1). A decrease in the hydrophobicity of the microenvironment between the alkyl-pyrazine and BSA was detected by synchronous fluorescence spectra, which revealed that alkyl-pyrazines were mainly bound on the sites of tyrosine and tryptophan in BSA. The UV-vis absorption spectra and circular dichromatic (CD) spectrum revealed that alkyl-pyrazines could induce polarity and conformation change of BSA. The above results indicated that the structure of the flavor homologues can affect their release in food matrices.